I have a few of these. just one out of the 4x is abit discolored.
I think when they were originally released in the clear thick "Library" poly plastic that came with it, if kept inside over time, this is what made it "discolored/brown"???

I could be wrong? this what I was told years back.

I have, just one copy, an all BROWN, not discolored, but originally issued like this, Manitou Shaped Goat!!!!!!!!! any offers!?? ha,ha,ha....